A tracking system in surgery is required in order to navigate a pre-operative plan relative to the patient's anatomy. The tracking system is generally used to track the patient's anatomy during the surgery and to navigate hand-operated surgical tools or a robot-assisted surgical tool.
Current surgical tracking systems in use rely upon determining the poses (position and orientation) of targets, such as infrared-emitting diodes or retroreflective spheres, which are attached to instruments or fixed into bone. An industry leader in producing such systems is NDI who have a medical product line consisting of two families of tracking systems, namely Polaris and Aurora. Details of the Polaris system can be found at: http://www.ndigital.com/medical/products/polaris-family/. The Polaris tracking system tracks the 3D position and orientation of active or passive markers attached to surgical tools with optical measurement technology. Details of the Aurora system can be found at: http://www.ndigital.com/medical/products/aurora/.
However, there are several significant drawbacks to current systems for tracking patient anatomy. Current optical tracking systems require a clear line of sight in order to “see” their targets. Optical tracking systems can be obtrusive and interfere with the surgical workflow because surgical staff must not occlude the camera's line of sight. These cameras are normally mounted at some distance from the patient. As the surgical working area is already somewhat small and compact, this makes it very difficult for surgical staff to work without blocking the cameras. This is perhaps the reason that is most noted by surgeons who express why navigation and robot-assisted systems are not adopted for most procedures in which they could be of value.
Also, many current intra-operative tracking systems require tracking devices to be rigidly mounted to the patient's bones of interest. This means that stab incisions are made in order to gain access to bone so that tracking targets can be drilled into the bones. These installation sites are most often not part of the surgical incision and exposure. Thus, they are considered to be additional morbidity which must be healed, and sources for increased risk of infection.
Cost also plays a significant role in the adoption of surgical systems. There are three elements of cost including initial capital cost (current tracking systems can easily cost $100,000 or more), replacement and maintenance costs, including sterilization and the cost of operating room time. Thus, cost is a significant factor for smaller and more remote medical establishments.
The tracking targets of current tracking systems require occasional replacement due to breakage and wear from being inside of the surgical field. Many popular optical trackers use passive retro-reflective targets that must be discarded and replaced after each surgery, which accounts for significant waste and expense. Additionally, the re-usable electronic targets and their bone mounting hardware must be sterilized using means that are safe to electronic equipment. Each of these targets has at least two parts for bone mounting and also require batteries which must be replaced for each surgery.
Most surgical procedures can begin immediately following incision and exposure. However, the most common surgical tracking systems are optical and require some setup of the camera for line of sight, and significant setup of the tracking targets for installation into bone, as described in above. This adds significant operating room time, which increases costs significantly to hospitals and the healthcare system. Tracking systems that are not optical, such as electromagnetic or ultrasonic, still require installation of targets, receivers or emitters in anatomy as described above.
Most current tracking technologies have fixed resolutions. For example, optical systems, which are the most commonly used tracking technology, have camera chips with a fixed number of pixels and pixel dimensions. Moreover, all current tracking systems navigate by position/orientation, which requires mathematical reduction to position coordinate and orientation angles, or geometric fitting such as least squares algorithms. These methods require complex calibration, and induce measurement error.
All current tracking systems, be they electromagnetic, optical, or ultrasonic are susceptible to interference from one or more electromagnetic, radio, sonic, or light sources. In particular, electromagnetic systems can also be impacted by metal surgical tools, operating table, and other metallic objects.
It would be very advantageous to provide a surgical navigation system which avoids the above-mentioned limitations and drawbacks and provides an economically cheaper alternative to current surgical navigation systems.